Climate Change Overview

Under the Australian Government plans to implement the Carbon Farming Initiative, there is a clearly identified need for modification of NRM plans to integrate climate change adaptation into regional planning processes.

When considering climate change impacts in WA Rangelands sub-regions, it is important to have an understanding of the broad agricultural, climatic and ecological zones that it encompasses. The highest level of regionalisation for Australia is the four super-clusters, which are divided into eight Clusters and 15 Sub-Clusters. This amalgamation (aligned as far as possible with existing NRM boundaries) preserves the detail of existing climatic zones and permits a coherent future projection to be described for each.

The Monsoonal North West sub-cluster, comprising NRM regions in Western Australia and the Northern Territory, commonly known as the tropical ‘top end’. This region experiences a pronounced wet and dry season. The Monsoonal North West covers tropical rainforests, wetlands and arid rangelands of the Northern Territory, and the steep mountain ranges of the Ord and Fitzroy River catchments of the Kimberley. Bordering along the north is the Timor Sea, while the Gulf of Carpentaria lies along the eastern edges. There is an extensive series of river systems in this cluster, including the Liverpool, Alligator, Daly, Finke, McArthur, Roper, Todd and Victoria Rivers.

The Rangelands North sub-cluster comprises NRM regions in four States and the Northern Territory, extending from the Indian Ocean to northwestern New South Wales. This vast region contains many varied landscapes, including the ranges of the Pilbara and ‘The Centre’; hence much of the iconic ‘Outback’. Many Indigenous Australians live in this region. Cattle grazing is an important agricultural activity. Rainfall systems vary from seasonally reliable monsoonal influences in the far north of the sub-cluster through to very low and variable rainfall patterns in much of the centre.

The Rangelands South sub-cluster comprises parts of NRM regions in three States, extending from the Indian Ocean to the Great Australian Bight and to western New South Wales. The split of Rangelands is motivated by the bioregions that result from the seasonal rainfall distribution. Much of the South regularly receives rainfall in winter, with only intermittent rainfall in other seasons. Many Indigenous Australians live in this region. Cattle and sheep grazing are important agricultural activities.

Future climate predictions

Key messages for future climate predictions for these three sub-clusters are:

Average temperatures will continue to increase in all seasons (very high confidence).

More hot days and warm spells are projected with very high confidence.

Increased intensity of extreme rainfall events is projected, with high confidence.

Mean sea levels will continue to rise and height of extreme sea-level events will also increase (very high confidence).

On annual and decadal basis, natural variability in the climate system can act to either mask or enhance any long-term human induced trend, particularly in the next 20 years and for rainfall.

Changes to summer rainfall are possible but unclear. Winter rainfall is projected to decrease in the south with high confidence.

A harsher fire-weather climate in the future (high confidence).

Climate change observed

Australia’s climate can vary greatly from one year to the next. Figure 2 presents the main influences upon the Australian climate. Influences will have varying levels of impact in different regions at different times of year, and these influences can all be impacted by shifts in global atmospheric and oceanographic circulation, expected to be in part influenced by human induced changed to the make-up of gases in the atmosphere.

In terms of climate changes that have already been observed on long term averages, the Climate Change in Australia website, run cooperatively between the CSIRO, Department of Climate Change & Energy Efficiency and the Bureau of Meteorology, states that Australia’s climate has warmed since national records began in 1910, especially since 1950. Mean surface air temperature has increased by 0.9°C since 1910. Daytime maximum temperatures have increased by 0.8°C over the same period, while overnight minimum temperatures have warmed by 1.1 °C. The warming trend occurs against a background of year-to-year climate variability, mostly associated with El Niño and La Niña in the tropical Pacific.

Temperature

The number of extreme heat records in Australia has outnumbered extreme cool records by almost 3 to 1 for daytime maximum temperatures, and almost 5 to 1 for night-time minimum temperatures. Very warm months that occurred just over 2 per cent of the time during the period 1951 to 1980 occurred nearly 7 per cent of the time during 1981 to 2010, and around 10 per cent of the time over the past 15 years. At the same time the frequency of very cool months has declined by around a third since the earlier period. The duration, frequency and intensity of heatwaves have increased across large parts of Australia since 1950. There has been an increase in extreme fire weather, and a longer fire season, across large parts of Australia since the 1970s.

Rainfall

Rainfall averaged across Australia has slightly increased since 1900, with a large increase in north-west Australia since 1970. A declining trend in winter rainfall persists in south-west Australia. Autumn and early winter rainfall has mostly been below average in the south-east since 1990.

Oceans

Sea-surface temperatures in the Australian region have warmed by 0.9°C since 1900. Global mean sea level increased throughout the 20th century and in 2012 was 225 mm higher than in 1880. Rates of sea-level rise vary around the Australian region, with higher sea-level rise observed in the north and rates similar to the global average observed in the south and east.